One of the main problems in power line carrier communication is how to modulate, demodulate, and process a communication signal in a very complex power noise environment. At present, many chips applied to power line communication are successively released, for example, PL31 series products available from Echelon Company in USA, and ST7538 chips available from ST Microelectronics Company in Switzerland, and these chips have made great contribution to the development of power line carrier communication.
FIG. 1 is a schematic structural diagram of a conventional power line carrier communication system. As shown in FIG. 1, in the system, a carrier signal of a power line coupling circuit 15 is amplified by a receiving front-end circuit in an analog front-end circuit 14, then the carrier signal is directly fed into a power line transceiver 13 to perform an analog-to-digital conversion under the control of a central controller 12 and demodulation through a digital signal processor (hereinafter referred to as “DSP”). With regard to a digital signal of an application system 11, under the control of the central controller 12, the power line transceiver 13 modulates the digital signal and a digital-to-analog circuit converts the digital signal into an analog carrier signal, then the analog carrier signal is directly amplified through a transmitting amplifier in the analog front-end circuit 14 and sent out through the power line coupling circuit 15. The system structure as shown in FIG. 1 is simple, and the effect is not desirable, e.g., it can only apply to a power noise environment with low interference, can only use a single modulation mode, and uses the general purpose DSP, which has relatively high manufacturing cost.
FIG. 2 is a schematic structural diagram of another conventional power line carrier communication system. As shown in FIG. 2, an analog front-end circuit 21 bandpass filters a carrier signal, the carrier signal is transmitted to a frequency-shift keying (hereinafter referred to as “FSK”) demodulator 23 via an intermediate frequency filter 22 to perform demodulation, and then the demodulated data are provided to a micro-controller to perform a processing via a serial communication interface 24. A digital signal is provided to an FSK modulator 25 via the serial communication interface 24 to perform modulation, filtered by a transmitting filter 26, then the modulated carrier signal is filtered and amplified through the analog front-end circuit 21, and sent out. The frequency of the FSK modulator or FSK demodulator and the parameter of each of the filters are controlled by a control register 27. This technical solution is to perform an external processing with transmitting data to a micro-controller via the serial communication interface. It increases the complexity and manufacturing cost of related products, and this technical solution may be only used in the FSK modulation mode. In addition, the solution of performing modulation and demodulation on a power communication signal in a phase shift keying (hereinafter referred to as “PSK”) modulation mode may also be used. But just like the FSK modulation mode, it can be only used in the PSK modulation mode.